1. Field of the Invention
The present invention relates to a headlamp, and more particularly to a headlamp employing a light-emitting diode.
2. Description of the Background Art
Conventionally, a light bulb was used for a headlamp mounted to a bicycle or the like, as in Japanese Utility Model Laying-Open No.02-031003. In recent years, however, with advancement of semiconductor elements and from the standpoint of low power consumption, a light-emitting diode has been adopted. In the headlamp employing the light-emitting diode, the light-emitting diode is mounted on a substrate portion and arranged within a prescribed casing, and is provided with necessary power from a battery housed in a battery case within the casing to turn on a light.
When the intensity of the light emitted from the light-emitting diode is increased to provide brighter light, heat is also generated from the light-emitting diode. If the temperature of the bonded portion of the light-emitting diode increases, luminous efficiency of the light-emitting diode decreases, leading to shortening of its life as well. Thus, it is desirable to provide a heat sink to absorb and dissipate the generated heat so as to suppress the increase in temperature of the bonded portion of the light-emitting diode.
Further, soldering for bonding the light-emitting diode to the substrate portion increases the temperature of the substrate portion, and the generated heat will affect the elements mounted on the substrate portion, including the light-emitting diode.
Thus, in order to protect the light-emitting diode and other elements mounted on the substrate portion from the heat, the substrate portion is made, e.g., of an aluminum plate having heat-dissipating capability, and a copper foil formed on the aluminum plate with an epoxy resin interposed therebetween. This means that the light-emitting diode is mounted on the aluminum plate with the epoxy resin and the copper foil interposed therebetween.
With the conventional headlamp employing the light-emitting diode, however, the heat dissipated from the substrate portion will remain around the substrate portion, making it difficult to suppress the temperature increase of the substrate portion.
Further, since the epoxy resin is disposed on the aluminum plate, sufficient conduction of the heat generated from the light-emitting diode or the heat upon soldering the light-emitting diode to the aluminum substrate portion cannot be expected, leading to degradation of the light-emitting diode and others.